1. Field of the Invention
This invention pertains to an electronic ballast system for gas discharge tubes. In particular, this invention relates to an electronic ballast system for fluorescent light sources which provides a high efficiency in transforming electrical energy into the visible bandwidth of the electromagnetic spectrum. More in particular, this invention directs itself to a transistorized electronic ballast system for fluorescent light sources. Still further, the subject invention concept provides an electronic circuit for fluorescent light sources which converts sinusoidal energy into rectangular pulses having a low duty factor at ultrasonic frequencies. Additionally, the subject invention relates to a transistorized electronic ballast system which reduces the use of electrical energy by as much as 50% with respect to some other commercially available ballast systems while maintaining substantially the same light output. Further, the subject electronic ballast system is directed to a system which minimizes weight, volume, and component elements to increase reliability, adaptability to currently available fluorescent tubes and minimizes manufacturing costs. Still further, the subject electronic system provides a unique circuitry where the gas discharge tube is incorporated within the circuit to provide the dual role of producing visible light as well as to dampen oscillations produced in the primary winding of a transformer when its current is interrupted as the transistor is switched to an "off" mode.
2. Prior Art
Ballast systems for gas discharge tubes and fluorescent light bulbs in particular are known in the art. However, in some prior art ballast systems, such operate at relatively low frequencies in the order of twice the line or power source frequency. Such prior art ballast systems have the disadvantage of providing a flicker type effect.
In other prior art ballast systems, the duty cycle of the electronic components is relatively high. Thus, such has led in the past to overheating of the electronic components contained within the ballast system and has caused failure of such prior art ballast systems over relatively shortened lifetimes.
In other prior art ballast systems, the number of components contained within the circuit is relatively large. This large number of components has led to such prior art ballast systems having a relatively large volume. The large volume has been due in part to the number of electronic components in such prior art ballast systems in combination with components used for dissipation of heat due to the disadvantageous thermal effects resulting from the high duty cycles.
In many prior art type ballast systems, the number of electrical components is high which results in a generally lower reliability as well as an increased manufacturing cost including additional labor costs.
Other types of prior art ballast systems generally operate at relatively low frequencies and have a low operating efficiency, which provides for approximately one-half the visible light output found in the subject invention electronic ballast system for the substantially the same electrical power input.
In some prior art systems an electronic ballasting system using transistor elements is provided. However, in some such prior art systems, a coil is used in series with a capacitor to supply the energy to the fluorescent system. Thus, in such prior art systems, the core must produce the charge/discharge of the overall system, but does not contribute to the energy that serves to drive the fluorescent tube and produce the visible light. In some such prior art systems, the electrical energy expenditure is increased due to the fact that energy must be supplied during the interval of the pulses in order that the plasma within the fluorescent tube does not become extinguished. Additionally, such prior art systems rely on saturation of the transformer magnetic core and the transistor to obtain an undriven square wave power oscillator converter. In such cases, the "on" time of the transistor is determined by the voltage induced in the secondary winding which is fixed by the transformer as well as the combination of the supply voltage and the turn ratio between the primary winding and secondary winding of the transformer. However, in such cases, the current is applied to the base of the transistor has substantially the same wave shape as the voltage pulse produced at the primary winding with the exception that at the instant of saturation, the transformer primary impedance quickly drops to substantially a zero value. This drop in impedance causes a steep rise in the collector current which results in a high collector current spike at the end of the conducting cycle which causes increased energy dissipation.